The risks associated with using wastewater for irrigation through the conventional over-ground method can be tackled through subsurface techniques using a sand-growth profile.
Secondary use of wastewater for irrigation purposes is a widely unused resource that could tip the balance for communities experiencing water-shortage situations.
Treated effluent water, as may be available from municipal sewage treatment plants or specialised small treatment plants designed for individual households, can produce high-quality water with a very low suspended solids content (visibly clear). Although not of drinking water quality, the effluent is a beneficial nutrient water source for plant growth.
The historical and regulatory public health issues have rightfully prohibited or limited wastewater reuse applications, because conventional, aboveground irrigation methods could not guarantee that public exposure would not occur due to potential bacteria and viruses that may still be viable in the wastewater sources.
Recent technical developments of sub-surface irrigation techniques through a sandgrowth profile provides built-in safety factors eliminating public health concerns and technical limitations for wastewater reuse. Wastewater really needs to be revisited as a valuable resource.
The EPIC System (www. epic-green.com) is based on the patented core technology known as the EPIC (Environmental Passive Integrated Chamber) water management system. The system combines an efficient irrigation and drainage system through non-pressurised, gravitydriven capillary physics of washed sand via direct interface of the EPIC subsurface pipe that never clogs. It is the sand medium and root zone that act as a natural and efficient biofilter. Within vegetated areas, grey water or wastewater (with no pre-filtration) and salt Water can be utilised in EPIC Systems as a subsurface irrigation resource – a benefit not seen in traditional systems.
The table illustrates a chemical composition perspective from two wastewater sources compared to the essential nutrient needs for plants.
Jonas Sipaila, Head of Innovation at EPIC Green Solutions said, “It is ironic that in our modern-day culture, we treat drinking water to impeccable standards and, then, re-contaminate the water with fertilisers so that plants can grow; and even more so, when in the desert environment, two-thirds of drinking water is used for agriculture and landscaping.”
When we look at the above table, it is obvious that contaminants measured in wastewater sources are nothing more than nutrients desired by plants (see items in green). So what are the red flags (see items in red) that bring public health concerns and how can they be rectified?
TSS (Total Suspended Solids) in layman’s terms is nothing more than cloudy water. Chemically, it is primarily cellulose and for pressurised sprinkler and drip irrigation, it poses a technical problem of plugging orifices and plugged emitters. The solution is to apply the water in nonpressurised, aerobic, sand-based, non-plugging, growing media and the TSS components recycle back to carbon dioxide and water.
Bacteria and potential viruses are a public health concern if wastewater is applied to the surface or through pressurised piping systems that can break and puddle at the surface for access to vectors or humans directly. This can be addressed by containing the water underground in a gravity-driven, unpressurised, sand-based system where sand filtration, nutrient uptake, and eventual biological decomposition in the plant root zone eliminates the infectious nature of pathogens.
A recent project that is currently being undertaken by EPIC Green Solutions is the treatment of the drainage runoff from the Los Angeles river basin that eventually flows to the Pacific Ocean. Using the EPIC System, this wastewater can be treated as it is filtered through the system that is installed below constructed parkland. The filtered water is used to irrigate the parkland and any excess water is, then, released into the Pacific Ocean in a purified state. The project is expected to be completed by February 2011.
In summary, while contaminants in wastewater are real, most contaminants are nutrients to plants. Pathogens are biologically neutralised if applied unpressurised to underground, aerobic sand environments. The end result is that wastewater becomes a valuable irrigation commodity.
